The goal of this project is to develop an in vitro microfluidic culture device that can be used to reproduce the mechanotransduction function of osteocytes, residing in native cortical bone tissues. As master regulators of homeostatic bone remodeling, osteocytes embedded are known to sense local compressive strain and initiate strain-dependent new bone formation by osteoblasts with sclerostin as one of major signaling molecules. Despite of this important understanding, there is currently no in vitro model that is capable of reproducing the physiological phenotype and mechanotransduction function of osteocytes for routine use in biomedical research and preclinical drug evaluation. We hypothesize that nanocomposite microbeads can be used to guide the re-establishment of 3D cellular networks of osteocytes harvested from mice during microfluidic perfusion culture. The microbeads will be engineered to mimic, upon their close packed assembly with osteocytes in the microfluidic culture chamber, the geometry and mechanical support function of the extracellular matrix of bones. The effectiveness of the assembly on guiding the re-establishment of 3D osteocyte networks will be evaluated. Our current microfluidic culture device will be modified to: (1) apply compressive cycling loading to 3D osteocyte networks reconstructed in the culture chamber and (2) reproduce the relationship between compressive strain and sclerostin expression, observed in a recent mouse ulna loading study. The in vivo mouse comparison will scientifically validate the use of the in vitro model, as a practical means of studying fundamental osteocyte biology. Furthermore, the comparison will provide new insight for follow-on development to culture primary human osteocytes and extend the microfluidic culture device'capability for simulating human bone remodeling. We envision that such a microfluidic human 3D bone tissue model may complement (or possibly replace) animal testing in preclinical evaluation of authentic human tissue response to drugs, for example, sclerostin antibodies that are being pursued to treat ~10 million osteoporosis patients and bone metastases with ~350,000 deaths per year in the U.S.

Public Health Relevance

As master regulators of homeostatic bone remodeling, osteocytes embedded in native bones are known to sense strain and initiate strain-dependent new bone formation by osteoblasts with sclerostin as a major signaling molecule. Despite of this understanding, there is no in vitro model that is capable of reproducing the physiological phenotype and mechanotransduction function of osteocytes for routine use in biomedical research and preclinical drug evaluation. This project will develop an in vitro microfluidic cultur device that can be used to reconstruct the 3D cellular network of primary mouse osteocytes and reproduce their mechanotransduction function previously observed in an in vivo mouse study. The in vivo comparison will scientifically validate the use of the in vitro model, as a practical means of studying fundamental mechanisms of osteocyte biology. Furthermore, this research will provide new insight for further development to culture primary human osteocytes and extend the microfluidic device'capability for simulating human bone remodeling. Such a microfluidic human 3D bone tissue model may complement (or possibly replace) animal testing in preclinical evaluation of human tissue response to drugs, for example, sclerostin antibodies that are being pursued to treat ~10 million osteoporosis patients and bone metastases with ~350,000 deaths per year in the U.S.